Such valve arrangements are used to actuate piston-cylinder arrangements. The piston is located at one end of a piston rod, with the result that the cross-sectional area of the space above the piston is larger than the cross-sectional area below the piston since the cross-sectional area of the piston rod is subtracted from this cross-sectional area. If high-pressure fluid is then fed to the spaces above and below the piston, the piston moves in a first direction because the force applied to the upper side of the piston by the high-pressure fluid is larger owing to the larger cross-sectional area than the force applied to the underside of the piston. If the space above the piston is relieved of pressure while this space and the fluid contained therein are connected to a reservoir vessel, also referred to as a low-pressure tank, which is at low pressure the piston moves in a direction opposed to the first direction. The piston rod is therefore extended out of the cylinder when the space above the piston is acted upon, and is retracted again when the pressure is relieved.
Any fluid may be used as the medium. Hydraulic oil is generally used but also compressed air in specific cases. The hydraulic oil can be made available here by specific high-pressure tanks whose design is insignificant for the present invention.
Such piston-cylinder arrangements are used, in particular, for activating the movable contact piece of high-voltage power switches, and can, of course, also be used in other applications in which components such as, for example, crane arms, shovels of shovel excavators and the like are to be moved.
The connection of the space above and below the piston to the high-pressure tank and the connection of the space above the piston to the low-pressure tank or to other connections is brought about by means of mostly electrically actuated valves, using a 3/2-way valve or two 2/2-way valves, the latter operating independently of one another.
Depending on the application case, the intention is to be able to achieve, for example, switching over which is without switching losses and during which a volume flow from the pressure connection to the low-pressure tank via both control edges is to be avoided during the switching process, and also to be able to achieve a flow resistance or volume flow of different magnitudes depending on the switched position, a short switching time or activation with a small pilot-control volume.
However, when a 3/2-way valve is used these requirements can frequently only be met inadequately or with a high level of expenditure on manufacturing and high manufacturing costs. If two 2/2-way valves are used, during switching over the open valve must firstly be closed before the closed valve is opened if a switching loss is to be avoided. However, in the case of pilot-controlled valves this requires at least two pilot-control valves with a suitable electrical actuation system with, for example, delayed or sensor-controlled triggering of the second valve. This entails further high costs and an unnecessarily long delay of the opening of the second 2/2-way valve after the first closes.